Two control voltages are generated, one increasing and another decreasing,
in response to the rise of the voltage of a condenser of a common
time-constant circuit. Based on the two control voltages, a first and a
second currents are formed, from which four different combinations of
currents are established. By feeding one of four combinations to each of
multiple differential output amplifier circuits each having a feedback
resistor, the multiple output amplifier circuits can be individually
started up or shut down without generating popcorn noise, using only one
single time constant circuit.